Image-forming developer

Abstract

An image-forming method using a developer comprising as the main component ferromagnetic and insulating toner particles. Said method comprises the steps of holding said developer on a delivery member by a magnetic force, causing the developer to tuft at the developing position and to fall in contact with an electrostatic latent image-supporting member, developing the electrostatic latent image and forming a toner image by the toner particles charged predominantly by mutual friction of the toner particles, and transferring the toner image onto a plain paper superimposed on the electrostatic latent image-supporting member by electrostatic transfer means. Said developer has a specific resistance of at least 10 14 Ω-cm and the potential decay ratio of the developed developer is lower than 50% as measured according to the method defined in the specification.

What is claimed is: 
     
       1. An image forming developer comprising toner particles, for use in a system wherein the developer is held on a delivery member by magnetic force and particles of the toner are charged while on said delivery member, an electrostatic latent image is produced on photoconductive material, said charged particles are contacted with said photoconductive material, and the developed image is transferred onto plain paper, said developer being characterized by: A. said developer comprising ferromagnetic and insulating toner particles having as the main component resin, said ferromagnetic particles being arranged on a part of the resin surface, said resin and ferromagnetic particles being chargeable to different polarities by friction with each other so that the toner particles are charged by mutual friction in consequence of movement of said delivery member;   B. said developer having a volume specific resistance of at least 10 14  Ω-cm; and   C. said developer having a potential decay ratio of less than 50% when measured by (1) forming on zinc oxide photoconductive material a layer of the developer of a predetermined thickness,   (2) erasing the electrostatic latent image on said photoconductive material which served to form said layer, so as to reveal the potentials of said layer,   (3) measuring the potentials V 1  and V 2  of said layer after one minute from dark decay and after three minutes from the succeeding light decay, respectively, and   (4) determining the decay ratio on the basis of (V 1  -V 2 )/V 1  ×100(%).